1. Field of the Invention
The present invention relates to a semiconductive rubber composition and a conductive rubber roller composed of the semiconductive rubber composition. More particularly, the conductive rubber roller is mounted as a developing roller or the like in image-forming apparatuses such as a copying apparatus, a printer, and the like.
2. Description of the Related Art
In recent years, in the printing technique using the electrophotographic method, a high-speed printing operation, formation of a high-quality image, formation of a color image, and miniaturization of image-forming apparatuses have been progressively made and become widespread. Toner holds the key to these improvements. To satisfy the above-described demands, it is necessary to form finely divided toner particles, make the diameters of the toner particles uniform, and make the toner particles spherical. Regarding the technique of forming the finely divided toner particles, toner having a diameter not more than 10 μm and toner not more than 5 μm have been developed recently. Regarding the technique of making the toner spherical, toner having not less than 99% in its deviation from a spherical form has been developed. To form the high-quality image, polymerized toner has come to be widely used instead of pulverized toner conventionally used. The polymerized toner allows the reproduction of dots to be excellent in obtaining printed matters from digital information and hence a high-quality printed matter to be obtained.
In correspondence to the improvement in the technique of forming finely divided toner particles, making the diameters of the toner particles uniform, making the toner particles spherical, and the transition from the pulverized toner conventionally used to the polymerized toner, conductive rubber members such as a conductive rubber roller constituting an image-forming apparatus adopting the electrophotographic method are demanded to have high-performance functions. For example, the conductive rubber member is demanded to have a uniform electrical characteristic on its the inner peripheral surface or on its in-plane. The conductive rubber member is also demanded to have a mechanical property which hardly changes for a long time. That is, it is necessary that the conductive rubber member does not wear nor modify for a long time when toner contacts the conductive rubber member or flows into a sliding contact portion of a member of the image-forming apparatus. The conductive rubber member is also demanded to have an electrical characteristic which hardly changes for a long time, when substances adhere to the surface thereof.
To comply with such a demand, the present inventors have developed various conductive compositions and proposed inventions disclosed in the following patent documents 1, 2, and 3.
In Japanese Patent Application Laid-Open No. 2003-183494, the polymer composition containing the epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer and the chloroprene rubber as its main components and sulfur and thioureas is disclosed in claim 2 and the example 4.
But the polymer composition has a comparatively high hardness and an insufficient elongation percentage. Thus the polymer composition has room for improvement in this respect. Therefore a developing roller composed of the above-described polymer composition has room for improvement so that a sufficient electrification amount is imparted to toner to obtain a high-quality image. In addition, the polymer composition has room for improvement of its wear resistance to prevent the occurrence of a disadvantage for a long time that toner leaks from a sealing portion of a toner cartridge as a result of wear of the developing roller owing to friction between it and the sealing portion of the toner cartridge.
In the patent document 1, although it is necessary to form an oxide film on the surface of the developing roller to form a high-quality image and reduce the friction coefficient of the surface thereof, no reference is made in the specification. Therefore the efficiency of the formation of the oxide film is not studied in the patent document 1.
In claims 1, 7 and the examples 13, 15 of the patent document 2, the conductive elastomer composition is disclosed in Japanese Patent Application Laid-Open No. 2004-176056 (patent document 2). The conductive elastomer composition contains the epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer mixed with the chloroprene rubber. The conductive elastomer composition contains further contains sulfur and thioureas used in combination for crosslinking. The conductive elastomer composition further contains the anion-containing salt having the fluoro group and the sulfonyl group. The conductive elastomer composition has a specified volume resistivity, compression set, and hardness.
The conductive elastomer composition disclosed in the patent document 2 has room for improvement in terms of its elongation percentage. Therefore a developing roller composed of the above-described conductive elastomer composition has room for improvement of its wear resistance to prevent the occurrence of a disadvantage for a long time that toner leaks from a sealing portion of a toner cartridge as a result of wear of the developing roller owing to friction between it and the sealing portion of the toner cartridge.
In the patent document 2, the conductive elastomer containing acrylonitrile-butadiene rubber (hereinafter referred to as NBR) instead of the chloroprene rubber is disclosed in paragraph [0037] and the examples 12, 14.
The epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer and the NBR have a high polarity respectively and mix with each other comparatively easily. The epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer is hydrophilic and contains chlorine, whereas the NBR is slightly hydrophilic and does not contain chlorine. Therefore the terpolymer and the NBR do not mix with each other nor disperse finely. Consequently the conductive elastomer composition is not sufficient in its strength and elongation percentage. The conductive elastomer composition has room for improvement in terms of its wear resistance so that the conductive elastomer composition can be used to compose a conductive member, for example, a developing roller which makes sliding contact with other member. More specifically, the developing roller rubs on the sealing portion of the toner cartridge.
In both modes of the conductive elastomer composition described in the patent document 2, it is difficult to stably form the oxide film by irradiating the surface thereof with ozone or ultraviolet rays. Therefore the conductive elastomer composition has room for improvement to allow the oxide film to be stably formed and a mass-production to be accomplished.
The conductive rubber composition is disclosed in Japanese Patent Application Laid-Open No. 2002-121376 (patent document 3). The conductive rubber composition contains the ethylene oxide-propylene oxide-allyl glycidyl ether terpolymer having the specified ratio among the monomers and molecular weight. The conductive rubber composition further contains the NBR and the epichlorohydrin rubber at the predetermined rate.
Similarly to the reason described on the conductive elastomer composition described in the patent document 2, the components of the conductive rubber composition of the patent document 3 do not disperse finely. Consequently the conductive rubber composition is not sufficient in its strength and elongation percentage. A member composed of the conductive rubber composition has room for improvement in terms of its wear resistance.
In the patent document 3, although it is necessary to form an oxide film on the surface of the developing roller to form a high-quality image, no reference is made in the specification. Therefore the efficiency of the formation of the oxide film is not studied in the patent document 3.
Patent document 1: Japanese Patent Application Laid-Open No. 2003-183494
Patent document 2: Japanese Patent Application Laid-Open No. 2004-176056
Patent document 3: Japanese Patent Application Laid-Open No. 2002-121376